When extension assist springs are used for hip prostheses, there is the problem that the hip bends when loading is relieved, which in the case of a normal gait cycle is desired as a means of facilitating bending, but when walking backward brings the wearer into an undesired situation.
Artificial joints, in particular knee joints, for orthoses or prostheses have an upper connection part and a lower connection part, which are connected to each other by way of a joint device. In the case of a knee joint, receptacles for an upper leg stump or an upper leg rail are arranged on the upper connection part, while a lower leg shaft or a lower leg rail is arranged on the lower connection part. In the simplest case, the upper connection part and the lower connection part are connected to each other pivotably by a single-axis joint. Only in exceptional cases is such an arrangement sufficient for ensuring the desired success, for example support in the case of the use of an orthesis or a natural gait pattern in the case of use in a prosthesis.
In order to represent as naturally as possible or be conducive to the various requirements during the various phases of a step, or in the case of other tasks, resistance devices which offer a flexion resistance and/or an extension resistance are provided. The flexion resistance is used to set how easily the lower connection part can be pivoted with respect to the upper connection part in the direction of flexion. In the case of a knee joint, the flexion resistance is therefore used to set how easily the lower leg shaft or the lower leg rail swings backward in relation to the upper leg shaft or the upper leg rail when a force is applied. The extension resistance retards the forward movement of the lower leg shaft or the lower leg rail and can form a stretching stop. In the case of other types of joint, such as the hip joint or the ankle joint, these statements apply in a way corresponding to the kinematic conditions.
It is possible by using settable resistance devices to adapt the respective flexion resistance and/or extension resistance to the user of the prosthetic or orthotic device or to make allowance for different gait or movement situations, in order to be able to offer an adapted resistance under changing conditions.
DE 10 2008 008 284 A1 discloses an orthopedic knee joint with an upper part and a lower part arranged pivotably thereon and assigned a number of sensors, for example a bending angle sensor, an acceleration sensor, an inclination sensor and/or a force sensor. The extension stop is determined in dependence on the sensor data determined.
DE 10 2006 021 802 A1 describes a control of a passive prosthetic knee joint with adjustable damping in the direction of flexion for the adaptation of a prosthetic device with upper connecting means and a connecting element to an artificial foot. The adaptation is for climbing stairs, a low-torque lift of the prosthetic foot being detected and the flexion damping being lowered in a lifting phase to below a level that is suitable for walking on level ground. The flexion damping may be raised in dependence on the changing of the knee angle and in dependence on the axial force acting on the lower leg.
DE 10 2007 053 389 A1 describes a method and a device for controlling an orthopedic joint of a lower extremity with at least one degree of freedom, with an adjustable actuator for adapting to walking situations that differ from walking on level ground an orthopedic device which has upper connecting means to a limb and an orthopedic joint arranged in a jointed manner distally in relation to the connecting means. In this case, a number of parameters of the orthopedic device are detected by way of sensors, the detected parameters are compared with criteria that have been produced on the basis of a number of parameters and/or parameter profiles and stored in a computer unit, and a criterion that is suitable on the basis of the parameters or parameter profiles determined is selected. On the basis of the criterion selected, bending resistances, bending extents, driving forces and/or how they vary over time are set in order to control special functions that deviate from walking on level ground. A tilting angle of part of the orthopedic device in space and/or a variation of a change in tilting angle of part of the orthopedic device may be used as parameters.
EP 1237513 B1 describes a prosthesis or orthesis with a control device and a sensor coupled therewith, which detects an angle of inclination with respect to a fixed line of a part connected to a joint. On the basis of the angle of inclination data, the movement properties of the joint change, that is to say the joint is braked or released.
Furthermore, the prior art discloses what are known as brake knee joints, in which the flexion resistance and extension resistance are mechanically increased as axial loading becomes greater. This is achieved in the simplest case by providing two braking surfaces which are pressed onto each other by a ground reaction force. Such a configuration cannot be used on the braking device for modern prosthetic knee joints with controlled resistance devices.